Method for thermally cutting tubing

ABSTRACT

A method for thermally cutting tubing, such as below an internal restriction in a tubing string located in a well bore, which comprises placing in the tubing at the desired location a mixture of finely granulated aluminum with an oxide of iron or other metal and igniting the mixture while applying a tensile load to the tubing string.

l 19g9 y m m ..l66/297 D United States Patent 1 1 011 3,727,685 Chestnutet al. 1 Apr. 17, 1973 [54 METHOD FOR THERMALLY CUTI'ING 2,436,0362/1948 Defenbaugh ..166/55 TUBING 2,746,550 5/1956 Miu=11611 ..l66/2552,839,143 6/1958 Alexander... ..l66/30l Inventors: Dwayne Chestnut,Lmleton, 3,076,507 2/1963 Sweetmon ..l66/297 C016; Clay A. Morris, SugarLand, 3,115,184 12/1963 Jackson .1 ..166/55 x Tex.

[73] Assignee: Shell Oil Company, Houston, Tex. Examiner-Dav? H BrownAttorney-Theodore E. Bieber et al. [22] Filed: Nov. 15, 1971 211 Appl.No.2 198,886 [57] ABSTRACT A method for thermally cutting tubing, suchas below 52 US. Cl. ..166/255, 166/297, 166/301, an internal resm'ctionin a tubing string located in a /5 5 well bore, which comprises placingin the tubing at the 51 Int. Cl ..E21b 47/00, E2lb 29/02 desiredlocation a mixture of finely granulated [58] Field of Search 166/250,255, 297, mini-1m with a OXide of iron 01' other metal and ignit-166/301, 315, 55, 63 ing the mixture while applying a tensile load tothe tubing string. [56] References Cited 6C 2m UNITED STATES PATENTSPATENTEU APR 1 "/1975 FIG. 2

FIG. 2

METHOD FOR THERMALLY CUTTING TUBING BAKCGROUND OF THE INVENTION Theinvention relates to a method of removing par tially collapsed ordeformed tubing by thermally cutting the tubing below the collapsedintervaland removing the tubing from the well bore.

DESCRIPTION OF THE PRIOR ART cutter. A chemical cutter, to be effective,requires a small diametrical clearance between its outer diameter andthe inner diameter of the tubing to be cut. If the tubing has beendeformed, that is, if the inner diameter has been reduced by asubstantial amount, a chemical cutter cannot be employed to cut thetubing below the deformity as it will not pass through the restrictionand still cut the tubing.

Another device that has been used is the string shot. The device islowered into the well bore by a wire line through the tubing to theinterval where the tubing is desired to be separated. The tubing is thenrotated clockwise by suitable means at the surface of the well boreuntil the tubing is torqued up". The device is subsequently detonated byelectrical means from the surface. By detonating the charge within thestring shot device, the tubing is hopefully untorqued, and, if theoperation is successful, the tubing will separate at a connection, thatis, by a pin unscrewing from a collar. The disadvantage of this deviceis that if the well casing has been deformed such that it is in contactwith the tubing, torque cannot be transmitted to the tubing below thispoint. In such a case the string shot device could not be used if it wasdesired to remove the tubing from the collapsed interval in the wellcasing.

A third device that has been employed to cut tubing in a well bore isthrough the use of mechanical cutters. These cutters can either beexternal or internal type cutters. An internal mechanical tubing cutterhas blades that extend and contact the inner wall of the tubing when thecutter is rotated. The disadvantage of this device is that it toodepends upon small diametrical clearance to be effective and, therefore,cannot be'effective if the tubing has been deformed to any great extent.

SUMMARY OF THE INVENTION The disadvantage inherent in these devices hasbeen advantageously solved by applicant's invention such that tubing maybe thermally cut below internal restrictions and removed from the wellbore so that the well may be repaired and restored to production.

It is a further object of this invention to thermally cut tubing whileapplying a tensile load to tubing in an upward direction enabling thetubing to separate while leaving a relatively smooth surface at the topof the tubing left in the well bore.

It is even a further object of this invention to restore the well toproduction after removal of the deformed tubing from the well borethereby precluding abandonment of a producing well that has significanthydrocarbon reserves or one that does not have sufficient reserves toprofitably justify redrilling a replacement for the abandoned well.

BRIEF DESCRIPTION OF THE DRAWING The nature of the invention will bemore fully appreciated with reference to the drawing in which:

.FIG. 1 is a sectional view showing a typical well in which the tubingstring is restricted preventing normal removal;

FIG. 2 is a sectional view illustrating the equipment that may beutilized in the practice of the invention for cutting and removing thetubing in the restricted interval.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1, a well isshown in communication with a hydrocarbon bearing formation 15 and theearths surface 13 through well casing 14. A tubing string 16 isinstalled in well casing 14 and is held in tension by a packer or tubinganchor 17. The tubing anchor 17 forms an integral part of tubing string16 and when properly actuated contacts well casing 14 such that thetubing string 16 may be maintained in tension. During normal operationif the tubing string 16 is required to be removed from well casing 14,the tubing anchor 17 is first released by rotation of tubing string 16and then tubing string 16 is removed using conventional procedure, wellknown in the art. In abnormal circumstances, a collapse 30 may occur inwell casing 14 such that a restriction 31 may develop in tubing string16, preventing release of tubing anchor 17 thereby precluding removal oftubing string 16 from well casing 14. Even further if tubing anchor 17is not installed in tubing string 16, conventional oil field tubularsare normally of the externally upset type which will also preventremoval of tubing string 16 from well casing 14. It is well known in theart that some oil field tubulars are flush in that they have acontinuous external diameter such that they may be removed from wellcasing 14 even though the collapse 30 exists in well casing 14. In thecase where the tubing string 16 has become restrained within well casing14 such that it has a restriction 31 a conventional workover unit 11 isinstalled over the well bore and tubing string 16 is placed in tensionwith suitable means with which unit 11 is equipped. While the tubingstring 16 is in tension wire line unit 12 is used to lower a free pointinstrument 18 that is electrically connected to wire line 19 into tubingstring 16. Read out equipment on board wire unit 12 is used to indicatethe interval in which tubing stirng 16 is restrained. Use of suchequipment is well known to those skilled in the art and will not bediscussed further.

When. it has been determined at which point or interval tubing string 16is restrained within well casing 14 a suitable tubing plug 26 is loweredinto tubing string 16 to a point below restriction 31 by suitable meanssuch as wire line 19 or a sand line from workover unit 11. Tubing plug26 may be any suitable means such as a conventional swab cup in its mostsimple form since all that is required in an obstruction within tubingstring 16 below restriction 31 capable of creating a bridge.

After setting a tubing plug 26 some distance below restriction 31, say15 to 20 and more preferably above the first tubing collar below casingcollapse 30, a conventional slim hole dump-bailer is lowered in tubingstring 16 by wire line 19 and is used to first place a predeterminedvolume of sand. A mixture of finely granulated aluminum with an oxide ofiron or other metal, which is sold under the trademark Thermit 27 isthen placed on top of the sand using wire line 19 and dump bailer.Preferably a volume of Thermit 27 equalling 6 to 18 of tubing volume isused. After placement of Thermit 27, dump bailer is removed from tubingstring 16. Wire line 19 is then used to lower electrical squib 29 andstarting Thermit into contact with Thermit 27 whereupon squib 29 isactivated using wire line unit 12 thereby igniting starting Thermitwhich ignites Thermit 27 upon reaching a temperature of approximately2200F. At a predetermined time after ignition of the starting Thermit,preferably l seconds, tension is pulled on tubing string 16 equalling5,000 to 30,000 pounds over the weight of tubing string 16 in wellcasing 14 from the surface to the interval where tubing string isrestrained in well casing 14. The resulting tubing cut after thisoperation is smooth, enabling conventional swaging techniques to be usedto enlarge well casing 14 such that a conventional overshot may then beused to retrieve the remainder of tubing string 16 from well casing 14without damage to well casing 14 from the thermal cutting of tubingstring 16.

In another embodiment of the invention, if the tubing is old or has alow yield point, a conventional chemical cutter may be used to cuttubing string 16 at a point above the collapsed interval 30 of wellcasing 14, say l to 20 feet, after which the tubing string 16 above thecut is removed from well casing 14. A tubing overshot 20, safety joint21, hydraulically operated jars 23, drill collars 24 are lowered in wellcasing 14 using a high strength work string 25 with workover unit 11.Preferably overshot 20 is of the type which has internal seals such thata pressure seal is present between tubing string 16 and overshot 20after overshot 20 has come into gripping contact with tubing string 16.After overshot 20 has engaged tubing string 16 a tensile force isappliedto tubing string 16. The tubing is then thermally cut using thepreviously described procedure.

We claim as our invention:

1. A method for thermally cutting tubing in well casing below aninternal restriction in said tubing, said method comprising the stepsof:

determining the interval in which the tubing is restricted; pluggingsaid tubing below said restriction by lowering suitable plugging meansin said tubing a predetermined distance below said restriction;

placing a predetermined volume of Thermit using suitable means belowsaid restriction and on top of said plugging means;

lowering starting Thermit and suitable ignition means into said tubingsuch that it is in contact with said thermit;

igniting said starting Thermit with said ignition means; applying atensile force to said tubing at a predetermined time interval afterigniting said starting Thermit; and

removing said tubing from said well.

2. The method of claim 1 wherein determining the interval in which thetubing is restricted is by freepointing said tubing string usingsuitable means.

3. The method of claim 1 wherein the volume of Thermit is equal to thevolume of 6 to 18 inches of tubing volume.

4. The method of claim I wherein plugging the tubing a predetermineddistance below said restriction is above the first tubing collaroccurring below the restriction.

5. The method of claim 1 wherein a tensile force of 5,000 to 30,000pounds over the weight of said tubing string is applied to said tubingstring.

6. The method of claim 1 wherein the predetermined time interval rangesfrom 5 to l5 seconds.

1. A method for thermally cutting tubing in well casing below aninternal restriction in said tubing, said method comprising the stepsof: determining the interval in which the tubing is restricted; pluggingsaid tubing below said restriction by lowering suitable plugging meansin said tubing a predetermined distance below said restriction; placinga predetermined volume of Thermit using suitable means below saidrestriction and on top of said plugging means; lowering starting Thermitand suitable ignition means into said tubing such that it is in contactwith said thermit; igniting said starting Thermit with said ignitionmeans; applying a tensile force to said tubing at a predetermined timeinterval after igniting said starting Thermit; and removing said tubingfrom said well.
 2. The method of claim 1 wherein determining theinterval in which the tubing is restricted is by free-pointing saidtubing string using suitable means.
 3. The method of claim 1 wherein thevolume of Thermit is equal to the volume of 6 to 18 inches of tubingvolume.
 4. The method of claim 1 wherein plugging the tubing apredetermined distance below said restriction is above the first tubingcollar occurring below the restriction.
 5. The method of claim 1 whereina tensile force of 5,000 to 30, 000 pounds over the weight of saidtubing string is applied to said tubing string.
 6. The method of claim 1wherein the predetermined time interval ranges from 5 to 15 seconds.